S1. Field protocols for vascular plants, butterflies and breeding birds.
Vascular plants
Plant surveys were performed by qualified botanists who received special training to
reduce among-observer variation. For each sample square of 1 km2, occurrences (presence
/ absence) of vascular plant species were surveyed along a 2.5 km transect that followed
existing trails wherever possible. If no trails existed, surveyors marked the transect route in
the field and plotted it on a map. At a sample square in a given year, transects were
inspected once in spring and again in late summer, assuring that data collection spanned a
large variation in flowering phenologies that likely influenced species detection [1].
Exceptions were sample squares at high altitudes with short vegetation period, where only
one inspection per field season was conducted. During each inspection of a sample square,
surveyors walked the transects in both directions and recorded all plant species within 2.5 m
to each side of the transects on the way forth and back, respectively. Sampling
characteristics of plant surveys were assessed in a previous study [2]: two botanists
independently assessed 23 transects; the mean of the relative differences between two
assessments was 7.9%, corresponding to a difference of 19.7 ± 4.9 species (mean ± SE),
with a total of 250 species recorded. For more information and quality measures on the field
methods, see [2] and [3].
Butterflies
The field protocol for butterflies was based on the British butterfly monitoring scheme [4].
Surveys of butterfly species occurrences (presence / absence) were performed by qualified
entomologists who received special training to reduce among-observer variation. At a sample
square in a given year, transects were inspected seven times between 21 April and 21
September in the lowlands, and four times between July and August above approximately
2000 m. The difference in numbers of inspections corresponds to the shorter flying season at
higher altitudes; sites at high and low altitudes received approximately equal sampling effort
per week of flight season, and differences in the number of visits should thus not bias the
results [1]. Surveys were conducted within separate time windows of 14 or 21 days,
depending on a seasonal schedule, following a standardized protocol. Butterfly surveys were
performed on the same transects as the surveys of vascular plants. Inspections of transects
were conducted during favourable weather conditions, i.e. sunshine during more that 80% of
the duration of the inspection, temperature of more than 13°C, and wind of less than 19 km/h
(Beauford level 1-2). During each inspection of transects, surveyors walked the transects in
both directions and recorded all day-flying butterfly species (including Hesperiidae and
Zygaenidae) within 5 m to each side of the transects on the way forth and back, respectively.
Detectability varied by species and averaged 88% per inspection [5]. For more information
and quality measures on the field methods, see [5-8].
Breeding birds
Surveys and surveying methods were largely identical to the Swiss Ornithological
Institute's common breeding bird survey [9,10]. Bird surveys were performed by qualified
volunteer ornithologists who used a territory mapping method [11]. Breeding birds were
surveyed using different transects than in vascular plants and butterflies, aiming at fully
covering each sample square and at detecting all breeding bird species. This resulted in
forested areas having greater transect lengths than did open sites. Transect lengths
averaged 5.1 km (range 1.2 - 9.4 km). In inaccessible regions with very steep slopes, sample
squares could sometimes not be fully covered. In such cases, any part of an area that was
impossible to sample was marked on a map. Depending on altitude, each square was
sampled two or three times between 15 April and 15 July. High altitude squares with less
than 10% forest cover were only visited twice, corresponding to the shorter breeding season
compared to low altitude squares. Mean detectability of birds across sites was estimated
89%, with a somewhat higher detectability at high altitude sites, in spite of receiving fewer
visits [10]. For more information and quality measures on the field methods, see [9,10,12].
References
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